1. Field of the Invention
The present invention relates to an electric power conversion circuit connected between an electric power supply source (such as a battery) and a multiphase electric rotary machine, and further relates to a control device for controlling the electric power conversion circuit to adjust control values for the multiphase electric rotary machine.
2. Description of the Related Art
It is known to control a switching element for an inverter unit based on a comparison result between an instruction voltage and a carrier wave to be supplied to an electric rotary machine as a control target. In the control operation, the inverter unit can supply an instruction voltage of an approximate sine curve to terminals of the electric rotary machine. However, because the output voltage of the inverter unit is varies rapidly when transmitted as binary, the voltage at a neutral node of the electric rotary machine is varied rapidly. This often generates common-mode noises and a large surge voltage.
In order to avoid the drawback of the control operation using the conventional inverter unit, for example, Japanese patent laid open publication JP 2005-295671 has proposed a conventional electric power conversion circuit in which the output terminal of each phase in a three phase electric rotary machine is connected to the output terminal of each of the converter unit. Each of the converter units in the conventional electric power conversion circuit converts the voltage of a capacitor connected in parallel to a pair of the output terminals of the electric rotary machine. The conventional electric power conversion circuit having the above structure suppresses the generation of a surge voltage because of supplying the voltage in a sine curve to each phase of the three-phase electric rotary machine.
By the way, each of the converter units in the conventional electric power conversion circuit for the three-phase electric rotary machine disclosed in JP 2005-295671 has four switching elements. That is, the conventional electric power conversion circuit for the three-phase electric rotary machine therefore has the twelve switching elements. The total number of the switching elements used in the conventional electric power conversion circuit disclosed in JP 2005-295671 is accordingly greater than that of the switching elements used in the previously-described inverter units. This increases the manufacturing cost of the electric power conversion circuit.